Hmm, well I always saw it as being used as a Java library within a Java project, but I guess there is no reason that it couldn't be stand-alone accessible through a cross-platform API like Thrift, or some kind of JSON-based REST API.
That being said, this is for the future.
What I thought you were going to ask is what Interfaces Store should implement.  I guess Store could implement Map<Set<String>, V> but not sure how useful it would be, or if we might have trouble supporting all of the functionality of that interface.
Ian.